Client Access Server 2007 (CAS)
Client Access server is one of the Role in Exchange 2007. Client access server is having some similarities with the old Front-End terminology (FE) servers Exchange 2003. CAS accepts connections from a variety of clients to allow them access to the Exchange Server infrastructure.
CAS is responsible for OWA, POP3, Active sync, web services and auto discovery.
CAS accepts connections to exchange 2007 from various clients and it is required in every Exchange 2007 Organization. CAS should be installed on a member server that has access to Global catalog server. When CAS is installed 4 directories will be installed by default. They are
- OWA: This virtual directory is used by OWA (Outlook Web Access) to access mailboxes on exchange 2007 server.
- Public: This virtual directory is used by OWA to access public folders running on Exchange 2000, 2003 and 2007.
- Exchweb: This virtual directory is used by OWA for accessing legacy mailboxes i.e. mailboxes on exchange 2000 & 2003.
- Exchange: This virtual directory is also for legacy mailboxes addition to exchange 2007 servers. CAS will automatically redirect 2007 users to OWA directory.
The ratio of CAS servers that needs to be installed in any organization should be 1 cas server for every 4 mailbox servers. This ratio is as per Microsoft.
CAS server is needed for each site where exchange mailbox servers are located and cas is the gateway for OWA clients. Though outlook (RPC/HTTP) communicates directly to the mailbox servers, it uses CAS to connect exchange mailbox and for services such as autodiscover server and availability service.
Autodiscover which is one of the service of CAS has been explained in Autodiscover section of this blog.